This invention relates to communication means for use in electronic systems. In particular, it relates to an omnidirectional optical interconnection communication network which uses a substantially planar optical waveguide to guide laser light communication in two dimensions, rather than in one dimension. Application of the invention is presently perceived to be in the field of integrated electronics as a substitute for wire connections, particularly in wafer-scale and multichip integrated systems.
In the world of integrated electronics, there is an ever increasing need for faster compute cycles. One attractive solution is wafer-scale integration, which is the direct use of a silicon wafer (gallium arsenide wafer or other suitable materials) as a substrate for the construction of an entire computing system, including processing, memory, input/output and other circuits. These systems could include processor, memory, floating point units, and input/output connections, and are particularly useful in signal processing and other applications where a large amount of processing capacity is required. Wafer scale integration provides improved speed while reducing the utilization of valuable circuit area for connection pads and input/output conditioning circuitry.
The complexity of interconnections and conductor routing between macrocells required for wafer-scale integration has been a severe problem and is a direct contributor to poor overall system yield. There have been many compromises in interconnection structures on the wafer but most fail because of the error prone nature of the interconnection medium. For example, global wire buses with close etches tend to be susceptible to shorts and open connections.
Current electro-optic systems utilize point-to-point communication, including the widespread use of fiber optics and other linear, effectively one-dimensional waveguides. Most point-to-point optical technologies are not inherently fault-tolerant, thus requiring complex logic and hardware to implement redundant sub-systems. Other proposed approaches to electro-optic communications, such as holography and movable mirrors, require precise alignment and considerable set up time, and hence are not optimal for communications at the processor/cache/memory interface level.
Given a set of equivalent components (macrocells) communicating on a wafer-scale computer system, the overall yield is a product of the component yield multiplied by the interconnection yield, hence there is clearly a need for high interconnection yield. The interconnection yield becomes critical when built-in testing techniques are used to detect and adapt to subsystem or component faults in wafer-scale systems. Recent work has shown that the use of pooled spares for fault circumvention is a viable technique for increasing yield in wafer-scale integration systems, but only where the interconnect yield can be made very high, much greater than the macrocell yield. Furthermore, slight improvements in interconnect yield can result in substantial improvements in overall system yield.
Three basic techniques currently exist for optically communicating between elements on a semiconductor surface: (1) direct connection with a point-to-point waveguide, (2) free-space unfocused broadcast and (3) free-space focused interconnection or imaging interconnections (holography).
The direct point-to-point connection method is efficient but fixes the topology in the same way as electrical bus connections fix the topology on the wafer. Free-space unfocused broadcast suffers from efficiency losses inherent in free-space transmission. In spite of its limitations, at least one experimental computer system has been built using a common free space optical bus. The use of holography as an approach to free-space focused interconnection is promising, but most work has utilized visible light and less is known concerning good holographic optical elements in the near infrared, where high speed optical technology has progressed. Work has also been reported on using deformable mirrors as an approach to free-space focused interconnection.
It is therefore desirable to produce a communication system for wafer-scale integration systems, and other similar high circuit density systems, that utilizes the advantages of optical communication methods while avoiding the difficulties attendant to the use of point-to-point, holographic, and other known techniques. It is further desired to avoid the need to construct a plurality of fixed point-to-point communication routes between various components or macrocells in a wafer-scale system, so that the communication system may be adaptable to changing topologies in a wafer-scale system.